Small, portable, generally triangular screw jacks have been employed for many years for the temporary support of mechanical objects during construction or other working operations. Screw jacks are especially useful in the support and alignment of pipe such as for positioning adjacent pipe sections and pipe fittings in precise alignment for welding operations. For the support of pipe, screw thread type pipe jacks are typically provided with various types of support heads depending upon the construction operation that is to be accomplished. For example, one type of support head may take the form of a V-shaped cradle that receives the pipe to be supported. This type of object support is known in the industry as a "V-head". Where the pipe is to be supported for rotation, a pipe support head having horizontally arranged, spaced rollers may be employed. This type of object support is referred to as a "roller head".
One particular type of screw jack is known as the "High/Low Screw Jack". It incorporates a generally triangular base incorporating a vertically oriented support tube. An elevation tube is received in telescoping relation within the support tube and may be manually raised or lowered to position the object support near its desired position. This adjustment may be referred to as a "coarse adjustment". Thereafter, the jack screw, which is located in telescoping relation within the elevation tube, is manipulated upwardly or downwardly to achieve precise positioning of the support head. This character of adjustment may be referred to as a "fine adjustment".
One of the disadvantages of high/low type screw jack mechanisms is the difficulty of maintaining the telescoping parts thereof in assembly during storage and handling. With the jack lying on its side during transportation, the vibration that typically occurs will often allow the telescoping parts to become separated. In such case, the loose telescoping components of the jack mechanism can become lost or damaged. Additionally, the jack screw, being unprotected by the elevation tube, can become damaged and its lubricant can become contaminated. In the event these types of pipe jacks are inverted for any reason, such as during handling in connection with construction activities, the telescoping components will simply slide apart and become separated. These components are sufficiently light-weight so that the jack mechanisms may be handled manually, but in a construction environment, these loose parts, especially the jack screw, can fall and constitute a hazard to workers. It is desirable, therefore, to provide a suitable means for maintaining the telescoping components of high/low type jack mechanisms in assembly while they are being handled or transported so that the telescoping components can not become separated from the jack and thus can not become lost or constitute a hazard to workers during construction operations.
Another disadvantage of these generally triangular pipe jacks is the difficulty of storage and handling. Since the pipe jacks are of generally triangular form, and since in most cases the legs thereof are fixed to the support tube, the space requirements for storage, handling, transportation, is quite significant. It is desirable, therefore, to provide a high/low screw type jack mechanism having support legs that are capable of being folded to substantially parallel relation with the support tube so that the space requirements for storage, handling, transportation, etc. is minimized.
Most high/low screw jack mechanisms employ a support tube of cylindrical configuration and also incorporate an elevation tube of cylindrical configuration being received in telescoping relation within the support tube. Typically, this type of jack mechanism incorporates a lock mechanism enabling the elevation tube to be secured in substantially immovable relation with the support tube. Typically, this type of lock mechanism is of the friction type and incorporates an externally threaded shaft that is received by an internally threaded receptacle of the support tube and is capable of being extended through an aperture in the support tube for frictional engagement with the outer cylindrical surface of the elevation tube. Although this type of friction lock is beneficial to retain the elevation tube in assembly with the support tube, there is no provision for securing the jack screw in assembly with the support tube.
The jack screw mechanism typically incorporates a drive nut that is received by the coarse Acme threads of the jack screw and being rotatably adjustable relative to the jack screw. The drive nut typically defines opposed operating handles for rotation thereof relative to the jack screw. In operation, the drive nut simply rests on the upper extremity of the elevation tube so that rotation of the drive nut achieves vertical movement of the jack screw and the support head carried by the jack screw. Thus, the jack screw, during handling or transportation of the jack can easily become separated from the other components of the jack mechanism and can become lost or damaged. For example, the Acme threads may become damaged to the extent that replacement of the jack screw becomes necessary. Further, the jack screw is often provided with a viscous paste-like lubricant that minimizes wear and friction as the drive nut is rotated. Should the jack screw become separated from the jack mechanism, obviously, the lubricant that coats the threads of the jack screw can become contaminated quite easily in the construction environment. When this happens, obviously it must be cleaned and relubricated. This becomes a disadvantage because the labor required to service the jack mechanism in this manner detracts from the commercial viability of the construction operation. It is desirable, therefore, to provide means for insuring against separation of the jack screw from the support tube and thus preventing the threads of the jack screw from becoming damaged or contaminated.
Portable, high/low screw jacks having folding legs for the purpose of minimizing the overall dimension thereof for purposes of storage and handling are known in the art. In most cases folding legs are simply attached to pivot connections that are provided upon the outer periphery of the support tube. In such cases, even when folded, the legs are disposed in angular relation with the support tube so that the folding jack mechanism is of substantial dimension at one end thereof. It is desirable, therefore to provide a folding leg mechanism for high/low type screw jacks that enable the legs to be folded to a position substantially parallel with the outer surfaces of the support tube to thereby minimize its overall dimension for efficiency of storage and handling.